Photovoltaic devices have been produced and used in the past with a certain amount of success. Devices of this type operate to produce a voltage in a non-homogeneous semiconductor, such as silicon, by the absorption of light or other electromagnetic radiation. In its simplest form, the photovoltaic effect occurs in the common photovoltaic cell used, for example, in solar batteries and exposure meters for cameras.
A photovoltaic cell consists of an n-p junction between two different semiconductor materials, namely, an n-type material in which conduction is due to electrons, and a p-type material in which conduction is due to positive holes. When light is absorbed near such a junction, electrons and holes are liberated in respective materials, the electrons which are liberated defining an electrical current flow along a path through the cell. The liberated electrons can then flow in an external circuit without the need for a battery as is required in conventional photoconductive devices. If the external circuit is broken, an open circuit photovoltage appears across the cell when the latter is subjected to light or other electromagnetic radiation.
While conventional photovoltaic cells have been satisfactorily used in a number of different applications, they are generally limited in power output because of the relatively large size which they must have to provide a usable power output. Moreover, they have a high production cost per unit of output power in comparison with other electrical devices. Since a cell of this type, to have a moderately high power output, must be relatively large, requires a relatively large operating space during use. This factor limits its portability and often requires special mounts which add to the overall cost per unit of output power derived from the cell.
Because of the foregoing limitations, a need has arisen for an improved energy conversion unit which uses the photovoltaic effect and which provides a high power output at low cost.